In a vacuum processing such as film, forming and the like, e.g., by sputtering or vapor deposition, there are cases where not only the pressure at the time of processing but also the compositions of residual gases in a vacuum chamber which serves as a processing chamber give a large influence on the quality of the film and the like. In order to analyze the compositions of this kind of residual gases (gas components), a quadrupole mass spectrometer has conventionally been used.
The quadrupole mass spectrometer is constituted by a sensor section which is detachably fitted to a test piece, and a control unit. As the sensor section, there has conventionally been used one which, supposing that the direction of fitting the sensor section to the test piece is in an upward direction, is provided with a disk-shaped, supporting body which is provided on a lower end of the sensor section; an ion detection section which is provided on the supporting body and which collects the ions; a quadrupole section which, is provided, on the ion detection section and in which four columnar electrodes are disposed at a circumferentially predetermined distance from one another; and an ion source which is provided on the quadrupole section and which has a filament and a grid to ionize the above-mentioned gas (see, e.g., patent document 1).
In order to apply an ionization voltage between the filament and the grid, and to form electric field in the quadrupole section, and to perform the like operations, the filament and the grid of the ion source, the quadrupole section, and the like are ordinarily connected by wiring to the connection terminals that are provided in the supporting body, and it is thus so arranged that electric power is supplied from the control unit through these connection terminals. As the wiring between the filament, the grid, the quadrupole section, and the connection terminals, there are used metallic wires such as copper and the like coated with covers made of ceramics in order to secure electric insulation. Therefore, in case the ion detection section, the quadrupole section, and the ion source are arranged from the side of the supporting body in the order as mentioned, as in the above-mentioned conventional example, a plurality of long wires are required, thereby resulting in a higher manufacturing cost, in addition, there is a disadvantage m that the assembling of the sensor section becomes troublesome,
By the way, as the above-mentioned filament, in place of a filament of tungsten make, there is recently used one which is manufactured by coating the surface of an Ir wire with an yttrium oxide, whereby the lifetime of the filament has largely been extended. As a result of prolonged lifetime of filament, it has become evident that the grid is contaminated by the adhesion of molecules and atoms in the vacuum atmosphere and that, due to this contamination, the sensitivity of measurement lowers.
As a method of cleaning the contaminated grid, there are known: electron collision system in which a voltage (about 300 V) is applied between the filament and the grid to cause the electrons to collide against the surface of the grid to thereby remove the molecules and atoms adhered, to the surface of the grid; and a so-called resistance heating system in which a current is caused to flow through the grid to thereby remove, by means of Joule heat, the molecules and atoms adhered to the surface of the grid (see, e.g., patent document 2).
When the resistance heating system is employed, it is necessary to form a closed circuit between the grid and the positive and the negative outputs from the DC power for resistance heating. In this case, connection will have to be made by separate further wiring to the connection terminals provided in the supporting body whereby the wiring to the grid becomes longer in the above-mentioned conventional example. Therefore, power loss becomes too large to be suitable for resistance heating. In addition, the quadrupole mass spectrometer becomes further complicated in construction and the assembling thereof becomes further difficult. As a result, the resistance heating system has conventionally rarely been employed.
On the other hand, when the electron collision system is employed, there are problems in that, during the time in which the electrons arc caused to be collided against the surface of the grid, mass analysis (measurement) by the mass analyzer cannot be made, and further that there is a possibility of giving rise to electric discharge if the pressure is high at the time of colliding the electrons at a high voltage.